TPITuned Port Injection discussion and questions. LB9 and L98 tech, porting, tuning, and bolt-on aftermarket products.
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When I put my TPI together I had it bored out to 52mm (actuall 51.85 with holley dominator blades), and the shaft has some bushing in it (oil lite or some name). The shaft was also milled thin.
I am quite sure there isn't an air leak in mine ... but who knows. I've checked so many other things, perhaps that has been bad all along. A can a carb cleaner should prove whether it is leaking or not.
Mark.
Quote:
Originally posted by maroguy1 I have the same problem on my 85 but it is not constant. Only happens in closed loop. Sometimes it will go from 500 to 800 sometimes just from 500 to 600. I have replaced it all have a burned 85 corvette prom, no emissions new injectors everything replaced except for the throttle body. I have read in other sites that the bearing that controls the throttle doesn't seal and leaks air which causes the idle hunt. It can also happen to aftermarket throttle bodies. So that is my next step until I decide to live with it.
I'll tell you about my exerience with the idle problem. It was exactly as you are describing. My setup is 87 IROC, headers, MSD ignition, rebuilt l98 heads, AFPR, 120,00 miles. Been having a bad idle problem since I bought the car. What finally fixed it for me was the following. Set air flow through the throttle body, cleaned IAC circuit, adjusted tps, new ford #24 lbh. injectors, fuel pressure to 43 lbs. at idle, fixed all vacuum leaks, changed from a 160 to 195 degree thermostat. The combination of these items fixed my problem. She finally now idles smooth as silk!
Hacked (both sides) and cleaned MAF with electic parts cleaner (reason for the hack was so I could clean real good); this seemed to help a lot. Noticed that with high fuel pressures (anything above 35psi) that car would run rich. When I set the airflow through throttle body, it was actually set at a higher rpm than suggested; only have the dash tach and would think it was set at about 650 rpm with timing connected and in nuetral. If car still seems to run rich, give it some more air! One way I could tell it was rich was the black soot under mufflers. Oh yea, the stat was 180df not 195df. Stat was an absolute must have change for me. I hope this helps, it sure took me a long time to get it right.
Ok I think I found my problem. All my parts are new tps maf iac. So I replaced the throttle body with a 52mm. I went to adjust the tps to .54. I would then flip the throttle it went from 4.5 to .59 no matter how much I adjusted it it wouldn't come back to the same voltage so I replaced it and reset the computer and so far it has been good. If I have the problem again I am going to replace it with an original gm unit. I have been using sorenson sensors and I am not too happy with them after this.
__________________ 81 camaro 350 ported & polished
85 iroc tpi 357 700r4 Sold!!!
05 GTO A4 fast as hell!!
08 Aveo 5 speed winter car
08 Ford edge toy hauler
No my car still surges, but not as bad. Turns out I had a bad regulator in my alternator and a weak battery. So the variable voltage was creating some of the surge. While it might have been 600-900 rpm surge, it is now 650-800 or so. Not as noticable.
It seems the surge is just a symptom of many things from a dirty TB, bad injectors, vac leak, and so forth. It's just the way the ECM deals with it as in it can't keep the idle constant.
The truck is parked for the winter, so testing is on hold for another season.
I was just wondering if anyone ever solved this mystery. I bought my z back in feb from a guy in pennsylvania and its had the same exact problem stated in this thread.. ive replaced the tb gasket, the iac, map sensor, tps sensor, plugs and wires. the car runs great but when ideling rpms jump up and down between 500-850 rpms... seems like it wants to be a 600 or 650 maybe but just doesnt stay there. no emissions codes no nothing. compression is ok, fuel pressure is ok and im 99.99 percent sure i do not have a vacuum leak.. is it possible that it could be an ignition coil, distributor cap and rotor button?
I also have a surging problem .. I've got and 89 formula firebird 305 TPI .
The car surges when i'm trying to hold a speed . When I accelerate It goes away. It does not do it at idle or when i let off the gas. Only when i'm trying to stay at a steady speed. in town at 25mph up to 60mph at a steady pace it will surge. I took it up to 70's 80's and 90mph and it won't surge at all at those faster speeds. anyone have any ideas.
Re: What causes an engine to "search" for an idle rpm?
You posted earlier that you started the car and within a few inutes just as the temp gauge started to move the idle droped to around 650 and began to hunt. There is a temp sensor in the head for the gauge and 1 on the front of the intake for the temp control to the ECM. You may be jumping in and out of closed loop. Check that sensor and the wiring around it. The sensor is only a resistance devce and a wire touching a hot spot can affect the signal to the ECU.
Re: What causes an engine to "search" for an idle rpm?
Quote:
Originally Posted by Formula11
I also have a surging problem .. I've got and 89 formula firebird 305 TPI .
The car surges when i'm trying to hold a speed . When I accelerate It goes away. It does not do it at idle or when i let off the gas. Only when i'm trying to stay at a steady speed. in town at 25mph up to 60mph at a steady pace it will surge. I took it up to 70's 80's and 90mph and it won't surge at all at those faster speeds. anyone have any ideas.
Time to throw in my $0.02. I'm having this exact same issue with my '92 Vert. The car is a stock 305 TPI.
I've messed with all the sensors, distributor etc. I've also put new stock 19# injectors. I've put in a new ECM. Checked for vacuum leaks. I'm stumped.
I have a theory....just a theory. This is a VERY common problem on the FBody's. I think something (or multiple somethings) are just a LITTLE out of spec. I think the problem actually lies with the ECM. Nothing physically wrong, but rather when things aren't exactly as it expectly them...it starts tripping the computer out and causing our "idle hunt"/"surging" problem.
